1. Title of the Invention
This invention relates to the selective transfer of elements from a transfer support to a reception support.
In particular, it relates to the transfer of partially or completely finished semiconductor chips from their initial substrate on which they were produced to a new substrate (or reception support) which may itself have been treated using microelectronic techniques.
The invention can be used for the transfer of chips, for example transfer of chips with a surface area of 1 cm.sup.2 from their initial substrate onto glass or onto a transparent substrate. It can also be used to transfer optoelectronic components such as VCSEL (vertical cavity lasers) or small pieces of III-V semiconductor from their initial substrate onto silicon wafers prepared using microelectronic techniques in order to obtain III-V semiconductor elements on silicon. In this case, the size of chips is usually smaller, for example of the order of 1 mm.sup.2 or less.
2. Description of the Related Art
The molecular bonding technique for bonding two surfaces made of semi-conductor material is known. Molecular bonding includes two types of bonding; namely hydrophilic bonding and hydrophobic bonding. In the case of hydrophilic bonding for the example of silicon oxide, bonding is the result of a change in --OH interactions at the surface of a structure to the formation of Si--O--Si bonds. The forces associated with this type of interaction are strong. The bonding energy is of the order of 100 mJ/m.sup.2 at ambient temperature and reaches 500 mJ/m.sup.2 after annealing at 400.degree. C. for 30 minutes (values obtained for bonding between native or hydrophilic SiO.sub.2 and unpolished thermal SiO.sub.2). The bonding energy is usually determined by the blade method described by W. P. MASZARA et al. in the "Bonding of silicon wafers for silicon-on-insulator" article published in J. Appl. Phys. 64(10), Nov. 15, 1988, pages 4943-4950. The bonding energy for bonding between deposited, polished silicon oxide and deposited, polished silicon oxide, is of the order of 1 J/m.sup.2 for annealing under the same conditions. However, if a hydrophilic treated surface is bonded by molecular bonding on a hydrophobic treated surface, very poor quality bonding is obtained and the bonding forces are very low; bonding energy of the order of 100 mJ/m.sup.2 after annealing at 400.degree. C. for 30 minutes.
Hydrophobic bonding is achieved by molecular bonding without an OH group. In the case of silicon, molecular bonding of hydrophobic wafers can also produce high bonding forces. For example, the work done by Y. BACKLUND et al. described in the "A suggested mechanism for silicon direct bonding from studying hydrophilic and hydrophobic surfaces" article published in J. Michromech. Microeng. 2 (1992), pages 158-160. This article shows that bonding forces of the order of 1 J/m.sup.2 are obtained after annealing at 400.degree. C., after bonding hydrophobic silicon wafers.